1. Field of Invention
This invention relates to methods and systems for reducing distortion in scanned images.
2. Description of Related Art
Distortion in scanned images is well known. For example, when book pages are scanned, the resulting digital images usually contain some geometric distortion or warping. This distortion is caused by book pages not being in uniform intimate contact with the scanning surface or platen surface of a scanner. For example, portions of book pages that are near the binding of the book are usually the portions that are not in intimate contact with the platen surface. Accordingly, distortion occurs in image parts corresponding to these portions.
Specialized scanners with height sensors have been suggested to achieve distortion-free scanning. For example, U.S. Pat. No. 5,659,404 discloses an image reading apparatus which reads document surface of an open-book-like document placed on a document platen in a face-upward condition and detects height of the document. U.S. Pat. Nos. 5,855,926, 5,969,829, 6,014,470 and 6,041,146 disclose similar apparatus. These apparatus are suggested largely to prevent image distortion from occurring.
Correction methods have also been developed to correct skew in scanned images with distortion. For example, U.S. Pat. No. 5,497,236 discloses a method and apparatus for correcting for splay. U.S. Pat. No. 5,187,753 discloses a method and apparatus for identifying and correcting for document skew.